1. Field of the Invention
The present invention relates generally to a vibratory barrel finishing machine, and more perticularly to a workpiece finishing machine of the type which includes a single or multiple vibratory barrel of an elongated elliptical form in plan view having semi-circular sloped sections on the opposite sides and straight sloped sections between the semi-circular sections, the machine further including guide means for allowing workpieces to be travelling along the passage inside the barrel.
2. Description of the Prior Art
The prior art vibratory barrel finishing machines of the type disclosed herein are described, for example, in the specifications of the Japanese published examined patent application No. 50-16558 and published unexamined patent application No. 53-141995. The machines disclosed in those specifications include a horizontal-bottom barrel or a simply upward-sloped barrel. In those prior art machines, a mixture of workpieces and abrasive media (which is referred to as "mass") travelling under vibration inside the barrel causes a turbulent flow, which prevents a regular and smooth travel of the mass through the various points of the barrel. Around the curved corners of the barrel in particular, the turbulent flow in the mass itself also prevents the mass from advancing forward, thus making it stagnant at the corners. In the worst cases, the mass being accumulated at the corners may be flooded beyond the barrel at the corners. A number of improvements have been made to eliminate the above problems. One of the improvements, for example, employs a plurality of vibration generators each carrying a pair of unblanced weights, but it does not meet the practical needs since it requires a high degree of accuracy to ensure a proper synchronized operation of the unbalanced weight pairs in each vibration generator, including lead angles of the weights with regard to each other, and a very delicate fine rotating of each unbalanced weight pair is therefore required to permit each corresponding vibration generator to supply proper vibrations to the barrel.
The prior art vibratory barrel finishing machine presents the above disadvantages and difficulties particularly when workpieces such as large-size workpieces and precision-surfacing workpieces are to be processed in bulk quantities. The impingement of the workpieces with each other very often occurs while travelling under vibration inside the barrel, causing the interfering workpieces to suffer indentations on the surfaces due to the impact. This makes the precision surface finishing practically impossible. In order to obviate from those problems, an elliptical-form vibratory finishing barrel with an arcuate bottom is proposed, and a workpiece suspension means is also proposed for holding individual workpieces suspended from the above. But, this technical improvement is not satisfactory because the constructional problem of the barrel still causes a mass flood or over flow to occur at the barrel corners. As a result, the workpieces held in suspension cannot travel at constant speeds through the barrel, or the advance of the workpieces is prevented at the particular locations of the barrel where the mass flow is hindered. When a flexible suspension means is employed, it must hold the adjacent workpieces in greatly spaced relation with each other in order to keep them from interferring with each other. This is however practically of less utility, since the quantity of workpieces to be processed at a time must be limited. Otherwise, the defective indentations due to the impact of the adjacent workpieces are inevitably caused.
A further improvement proposes the provision of a number of partitions inside the barrel, as disclosed in the Japanese published unexamined patent application No. 52-92190, for example. This improvement has been made to the annular vibratory barrel finishing machine type, in order to protect the workpieces from the impingement caused by the interference of the workpieces. However, that type of machine has an annular form barrel in which the time interval or cycle time of the mass travelling through the entire barrel is shorter, restricting the quantity of workpieces to be processed at a time to relatively small. If larger quantities of workpieces are desired to be processed, it would of course be possible to provide a large barrel, which however would require a larger machine frame to be built, thus requiring a larger floor space on which such machine should be installed. As an alternative solution, a longer-run annular barrel with a horizontal bottom is employed, in which a workpiece advance control plate is provided. However, this does not allow for the constant and smooth travel of the mass because in this case the turbulent flow in the mass is also caused at the particular locations of the barrel as mentioned earlier, and in some extreme cases there is an overflow or flood of the mass beyond the barrel at the curved corners. As a result, an excessive load is placed on the above workpiece advance control plate, thus causing damages such as impingement on the workpieces. This alternative solution does not meet the practical needs.